Twenty Twelve: better "no posts found" message and action for index view. If a...

Twenty Twelve: better "no posts found" message and action for index view. If a logged-in user can edit posts, show an appropriate message. Otherwise, show the normal "no posts found" message. See #19978.


git-svn-id: https://core.svn.wordpress.org/trunk@20006 1a063a9b-81f0-0310-95a4-ce76da25c4cd